In general, an electrostatic chuck using electrostatic adsorption is used in a holding mechanism of an object to be processed such as a semiconductor wafer in a plasma processing apparatus, and the electrostatically adsorbed object to be processed is subjected to a predetermined plasma process.
Examples of the holding mechanism of the object to be processed include two types including a type in which a high direct-current voltage is applied to an electrode plate disposed in the electrostatic chuck shown in FIG. 5, and a type in which the electrostatic chuck is held and a high direct-current voltage is applied to an electrode for generating plasma as shown in FIG. 6. For the sake of convenience, the former electrostatic chuck is referred to as a separated type, and the latter chuck is referred to as a coupled type.
As shown in FIG. 5, the separated type of holding mechanism of the object to be processed includes an electrostatic chuck 21 which electrostatically adsorbs the object to be processed (e.g., a semiconductor wafer), and a lower electrode 22 including aluminum whose surface is alumite-processed or coated with an insulating material such as ceramic. An upper electrode 23 is disposed above, parallel to, and opposite to the lower electrode 22 at a predetermined interval.
Moreover, the lower electrode 22 is connected to a high-frequency power source 25 via a matching circuit 24, high-frequency power is applied to the lower electrode 22 from the high-frequency power source 25, and plasma P is generated between the lower electrode 22 and upper electrode 23. This plasma P is collected onto a semiconductor wafer W via a focus ring 22a disposed in an outer peripheral edge of the lower electrode 22, and the semiconductor wafer is subjected to a plasma processing such as etching.
The electrostatic chuck 21 is formed by insulating materials such as a polyimide-based resin and ceramics, and an electrode plate 21a is disposed inside the chuck. The electrode plate 21a is connected to a high-voltage power source 27 which applies a direct-current voltage via a filter circuit 26, the high-voltage power source 27 applies a high direct-current voltage to the electrode plate 21a, and the semiconductor wafer is electrostatically adsorbed onto a front surface of the electrostatic chuck 21.
The filter circuit 26 includes, for example, a coil 26a, resistor 26b, and capacitor 26c, filters a high-frequency current from the high-frequency power source 25, and prevents the high-frequency current from turning onto a high-voltage power source 27 side.
Moreover, the lower electrode 22 is connected to a detection circuit 28. This detection circuit 28 measures a direct-current (DC) component generated in the lower electrode 22 to which the high-frequency power is applied. For example, as shown in FIG. 5, the circuit includes a coil 28a, resistor 28b, and capacitor 28c, and measures the direct-current component of a point A. At this measurement time, the circuit cuts the high-frequency current from the high-frequency power source 25, and prevents the high-frequency current from turning into the point A.
On the other hand, as shown in FIG. 6, the coupled type of holding mechanism of the object to be processed includes a constitution similar to that of the above-described separated type of holding mechanism of the object to be processed except that the lower electrode 22 also functions as the electrode plate of the electrostatic chuck 21. That is, the lower electrode 22 is connected to both the high-frequency power source 25 and high-voltage power source 27, and the high-frequency power source 25 applies the high-frequency power to the lower electrode 22 to generate the plasma P between the upper electrode 23 and lower electrode. Furthermore, the high-voltage power source 27 applies the high direct-current voltage to the lower electrode 22 to electrostatically charge the electrostatic chuck 21 and to electrostatically adsorb the semiconductor wafer.
Additionally, in addition to the function as the detection circuit of the direct-current component in the lower electrode 22 at the plasma processing time, the detection circuit 28 also has a function as a static eliminator circuit which eliminates charges remaining in capacitor components in the lower electrode 22 and matching circuit 24. For the separated type of holding mechanism of the object to be processed, a property as the static eliminator circuit is sometimes used to use the detection circuit 28 as life management means of the lower electrode 22.
That is, while the plasma processing is performed, the surface of the lower electrode 22 is sputtered, the alumite processing is scraped and stripped off, this stripped portion forms a closed circuit between the lower electrode 22 and upper electrode 23, and a current flows toward a detection circuit 28 side from the lower electrode 22.
When the current is measured by the detection circuit 28, the stripped degree (wear degree) of the lower electrode 22 by the sputtering can be grasped by the magnitude of the measured value, and further the life of the lower electrode 22 can be managed. The detection circuit 28 measures the direct-current component in the lower electrode 22, and the direct-current component is ideally in a 0V state at times other than times when the high-frequency power is turned ON/OFF or the high voltage is turned ON/OFF. Therefore, the current flowing through the lower electrode 22 at the plasma processing time can be grasped as the current which flows through the lower electrode 22 via the stripped alumite-processed portion. However, with the separated type of holding mechanism of the object to be processed shown in FIG. 5, depending on process conditions, while the semiconductor wafer is subjected to the plasma processing, for example, the detection circuit 28 functions as the static eliminator circuit, and a current i1 flows into the detection circuit 28 from the lower electrode 22. Therefore, a potential difference is generated between the lower electrode 22 and a focus ring 22a by the voltage drop of the lower electrode 22, and there has been a problem that this potential difference causes abnormal electric discharge between the lower electrode 22 and components such as the focus ring 22a. 
To avoid this, when the detection circuit 28 is disconnected, the abnormal electric discharge at plasma processing time can be prevented, but there is a disadvantage that the charges remain in the lower electrode 22. Moreover, when refrigerant remains to be circulated in a refrigerant channel in the lower electrode 22 at maintenance time, static electricity is generated by friction of the refrigerant with the refrigerant channel, the lower electrode 22 is charged, and this causes a problem of electric shock.
Moreover, with the coupled type of holding mechanism of the object to be processed shown in FIG. 6, since a closed circuit is formed between the high-voltage power source 27 and detection circuit 28, as shown in the drawing, a current i2 constantly flows toward the detection circuit 28 from the high-voltage power source 27, the voltage applied to the lower electrode 22 from the high-voltage power source 27 drops, and there is a problem of deterioration of the electrostatic adsorption function of the electrostatic chuck 21. Furthermore, to avoid this, when the detection circuit 28 is disconnected, there is a problem of electrostatic charging in the lower electrode 22 in the same manner as in the separated type.